Etude de la composition initiale et du vieillissement des traces digitales: vers le développement d'une méthode de datation?

«Quel est l'âge de cette trace digitale?» Cette question est relativement souvent soulevée au tribunal ou lors d'investigations, lorsque la personne suspectée admet avoir laissé ses empreintes digitales sur une scène de crime mais prétend l'avoir fait à un autre moment que celui du crime et pour une raison innocente. Toutefois, aucune réponse ne peut actuellement être donnée à cette question, puisqu'aucune méthodologie n'est pour l'heure validée et acceptée par l'ensemble de la communauté forensique. Néanmoins, l'inventaire de cas américains conduit dans cette recherche a montré que les experts fournissent tout de même des témoignages au tribunal concernant l'âge de traces digitales, même si ceux-­‐ci sont majoritairement basés sur des paramètres subjectifs et mal documentés. Il a été relativement aisé d'accéder à des cas américains détaillés, ce qui explique le choix de l'exemple. Toutefois, la problématique de la datation des traces digitales est rencontrée dans le monde entier, et le manque de consensus actuel dans les réponses données souligne la nécessité d'effectuer des études sur le sujet. Le but de la présente recherche est donc d'évaluer la possibilité de développer une méthode de datation objective des traces digitales. Comme les questions entourant la mise au point d'une telle procédure ne sont pas nouvelles, différentes tentatives ont déjà été décrites dans la littérature. Cette recherche les a étudiées de manière critique, et souligne que la plupart des méthodologies reportées souffrent de limitations prévenant leur utilisation pratique. Néanmoins, certaines approches basées sur l'évolution dans le temps de composés intrinsèques aux résidus papillaires se sont montrées prometteuses. Ainsi, un recensement détaillé de la littérature a été conduit afin d'identifier les composés présents dans les traces digitales et les techniques analytiques capables de les détecter. Le choix a été fait de se concentrer sur les composés sébacés détectés par chromatographie gazeuse couplée à la spectrométrie de masse (GC/MS) ou par spectroscopie infrarouge à transformée de Fourier. Des analyses GC/MS ont été menées afin de caractériser la variabilité initiale de lipides cibles au sein des traces digitales d'un même donneur (intra-­‐variabilité) et entre les traces digitales de donneurs différents (inter-­‐variabilité). Ainsi, plusieurs molécules ont été identifiées et quantifiées pour la première fois dans les résidus papillaires. De plus, il a été déterminé que l'intra-­‐variabilité des résidus était significativement plus basse que l'inter-­‐variabilité, mais que ces deux types de variabilité pouvaient être réduits en utilisant différents pré-­‐ traitements statistiques s'inspirant du domaine du profilage de produits stupéfiants. Il a également été possible de proposer un modèle objectif de classification des donneurs permettant de les regrouper dans deux classes principales en se basant sur la composition initiale de leurs traces digitales. Ces classes correspondent à ce qui est actuellement appelé de manière relativement subjective des « bons » ou « mauvais » donneurs. Le potentiel d'un tel modèle est élevé dans le domaine de la recherche en traces digitales, puisqu'il permet de sélectionner des donneurs représentatifs selon les composés d'intérêt. En utilisant la GC/MS et la FTIR, une étude détaillée a été conduite sur les effets de différents facteurs d'influence sur la composition initiale et le vieillissement de molécules lipidiques au sein des traces digitales. Il a ainsi été déterminé que des modèles univariés et multivariés pouvaient être construits pour décrire le vieillissement des composés cibles (transformés en paramètres de vieillissement par pré-­‐traitement), mais que certains facteurs d'influence affectaient ces modèles plus sérieusement que d'autres. En effet, le donneur, le substrat et l'application de techniques de révélation semblent empêcher la construction de modèles reproductibles. Les autres facteurs testés (moment de déposition, pression, température et illumination) influencent également les résidus et leur vieillissement, mais des modèles combinant différentes valeurs de ces facteurs ont tout de même prouvé leur robustesse dans des situations bien définies. De plus, des traces digitales-­‐tests ont été analysées par GC/MS afin d'être datées en utilisant certains des modèles construits. Il s'est avéré que des estimations correctes étaient obtenues pour plus de 60 % des traces-­‐tests datées, et jusqu'à 100% lorsque les conditions de stockage étaient connues. Ces résultats sont intéressants mais il est impératif de conduire des recherches supplémentaires afin d'évaluer les possibilités d'application de ces modèles dans des cas réels. Dans une perspective plus fondamentale, une étude pilote a également été effectuée sur l'utilisation de la spectroscopie infrarouge combinée à l'imagerie chimique (FTIR-­‐CI) afin d'obtenir des informations quant à la composition et au vieillissement des traces digitales. Plus précisément, la capacité de cette technique à mettre en évidence le vieillissement et l'effet de certains facteurs d'influence sur de larges zones de traces digitales a été investiguée. Cette information a ensuite été comparée avec celle obtenue par les spectres FTIR simples. Il en a ainsi résulté que la FTIR-­‐CI était un outil puissant, mais que son utilisation dans l'étude des résidus papillaires à des buts forensiques avait des limites. En effet, dans cette recherche, cette technique n'a pas permis d'obtenir des informations supplémentaires par rapport aux spectres FTIR traditionnels et a également montré des désavantages majeurs, à savoir de longs temps d'analyse et de traitement, particulièrement lorsque de larges zones de traces digitales doivent être couvertes. Finalement, les résultats obtenus dans ce travail ont permis la proposition et discussion d'une approche pragmatique afin d'aborder les questions de datation des traces digitales. Cette approche permet ainsi d'identifier quel type d'information le scientifique serait capable d'apporter aux enquêteurs et/ou au tribunal à l'heure actuelle. De plus, le canevas proposé décrit également les différentes étapes itératives de développement qui devraient être suivies par la recherche afin de parvenir à la validation d'une méthodologie de datation des traces digitales objective, dont les capacités et limites sont connues et documentées. -- "How old is this fingermark?" This question is relatively often raised in trials when suspects admit that they have left their fingermarks on a crime scene but allege that the contact occurred at a time different to that of the crime and for legitimate reasons. However, no answer can be given to this question so far, because no fingermark dating methodology has been validated and accepted by the whole forensic community. Nevertheless, the review of past American cases highlighted that experts actually gave/give testimonies in courts about the age of fingermarks, even if mostly based on subjective and badly documented parameters. It was relatively easy to access fully described American cases, thus explaining the origin of the given examples. However, fingermark dating issues are encountered worldwide, and the lack of consensus among the given answers highlights the necessity to conduct research on the subject. The present work thus aims at studying the possibility to develop an objective fingermark dating method. As the questions surrounding the development of dating procedures are not new, different attempts were already described in the literature. This research proposes a critical review of these attempts and highlights that most of the reported methodologies still suffer from limitations preventing their use in actual practice. Nevertheless, some approaches based on the evolution of intrinsic compounds detected in fingermark residue over time appear to be promising. Thus, an exhaustive review of the literature was conducted in order to identify the compounds available in the fingermark residue and the analytical techniques capable of analysing them. It was chosen to concentrate on sebaceous compounds analysed using gas chromatography coupled with mass spectrometry (GC/MS) or Fourier transform infrared spectroscopy (FTIR). GC/MS analyses were conducted in order to characterize the initial variability of target lipids among fresh fingermarks of the same donor (intra-­‐variability) and between fingermarks of different donors (inter-­‐variability). As a result, many molecules were identified and quantified for the first time in fingermark residue. Furthermore, it was determined that the intra-­‐variability of the fingermark residue was significantly lower than the inter-­‐variability, but that it was possible to reduce both kind of variability using different statistical pre-­‐ treatments inspired from the drug profiling area. It was also possible to propose an objective donor classification model allowing the grouping of donors in two main classes based on their initial lipid composition. These classes correspond to what is relatively subjectively called "good" or "bad" donors. The potential of such a model is high for the fingermark research field, as it allows the selection of representative donors based on compounds of interest. Using GC/MS and FTIR, an in-­‐depth study of the effects of different influence factors on the initial composition and aging of target lipid molecules found in fingermark residue was conducted. It was determined that univariate and multivariate models could be build to describe the aging of target compounds (transformed in aging parameters through pre-­‐ processing techniques), but that some influence factors were affecting these models more than others. In fact, the donor, the substrate and the application of enhancement techniques seemed to hinder the construction of reproducible models. The other tested factors (deposition moment, pressure, temperature and illumination) also affected the residue and their aging, but models combining different values of these factors still proved to be robust. Furthermore, test-­‐fingermarks were analysed with GC/MS in order to be dated using some of the generated models. It turned out that correct estimations were obtained for 60% of the dated test-­‐fingermarks and until 100% when the storage conditions were known. These results are interesting but further research should be conducted to evaluate if these models could be used in uncontrolled casework conditions. In a more fundamental perspective, a pilot study was also conducted on the use of infrared spectroscopy combined with chemical imaging in order to gain information about the fingermark composition and aging. More precisely, its ability to highlight influence factors and aging effects over large areas of fingermarks was investigated. This information was then compared with that given by individual FTIR spectra. It was concluded that while FTIR-­‐ CI is a powerful tool, its use to study natural fingermark residue for forensic purposes has to be carefully considered. In fact, in this study, this technique does not yield more information on residue distribution than traditional FTIR spectra and also suffers from major drawbacks, such as long analysis and processing time, particularly when large fingermark areas need to be covered. Finally, the results obtained in this research allowed the proposition and discussion of a formal and pragmatic framework to approach the fingermark dating questions. It allows identifying which type of information the scientist would be able to bring so far to investigators and/or Justice. Furthermore, this proposed framework also describes the different iterative development steps that the research should follow in order to achieve the validation of an objective fingermark dating methodology, whose capacities and limits are well known and properly documented

Estimativa temporal de impressões digitais latentes : desenvolvimento de métodos espectroscópicos com aplicação quimiométrica e de imageamento químico por espectrometria de massas para a rotina forense

A Papiloscopia é uma área de Ciências Forenses que é responsável pela identificação humana, sendo as impressões digitais o elementos-chave, que são uma das principais e mais frequentes evidências físicas em investigações criminais. Um desafio para a análise das impressões digitais é o estabelecimento de sua datação (envelhecimento), ou seja, o período decorrido entre sua afixação na cena do crime e a análise do laboratório. O envelhecimento da impressão digital presente em uma cena de crime pode ser útil para discernir um evento ou situá-lo na linha temporal investigativa. No entanto, as impressões digitais são uma matriz biológica complexa com fatores de variabilidade intrínseca e extrínseca ao doador, sendo um desafio não apenas para identificar os componentes bioquímicos, mas também para entender seus padrões de envelhecimento. Para isso, os métodos analíticos guiaram esta tese em duas revisões: a primeira, foram selecionadas as classes de métodos mais utilizadas para análise de impressão digital e a segunda, quais componentes bioquímicos presentes nas amostras fornecem informações sobre a estimativa temporal das amostras. Em relação às classes de métodos, a espectrometria de massa provou ser a técnica promissora para análise de impressão digital, destacando a fonte de ionização/dessorção assistida por matriz (MALDI MS) como a mais usada. Com isso, um método MALDI MS foi desenvolvido com a aplicação de imagens químicas (IMS) que, a partir da seleção de íons dos componentes de maior intensidade nas amostras, permitiram a visualização de impressões digitais cinquenta dias após seu depoimento. A segunda classe de métodos mais utilizada foi a espectroscopia, na qual um método de Microespectroscopia de Infravermelho com Transformada de Fourier (μ-FTIR) foi desenvolvido para a análise de impressões digitais sebáceas monitoradas por uma semana, seguidas pelo uso do método não- supervisionado de análise linear discriminante (LDA). Observou -se que, apesar dos perfis do doador serem semelhantes, o método permitiu a elaboração de uma tendência de separação entre as amostras com base no tempo de deposição. E, além disso, foi possível separar as amostras por doador. Assim, este trabalho compõe um passo em direção à aplicação da ciência analítica à Papiloscopia como um recurso fundamental da justiça na geração de evidências robustas para a busca da verdade.Fingerprint Analysis is the area of Forensic Sciences that deals with human identification, having fingerprints as key elements, which are one of the main and most frequent physical evidences in criminal investigations. A challenge for the fingerprint analysis is the establishment of their aging, that is, the period elapsed between their affixation at the crime scene and the forensic analysis. The fingerprint aging estimation at a crime scene can be useful in discerning an event or placing it in time. However, fingerprints are a complex biological matrix with intrinsic and extrinsic variability factors to the donor, being a challenge not only to identify the biochemical components present, but also to understand their aging patterns. For this, the analytical methods guided this research in two reviews: the first selected the classes of methods most used for fingerprint analysis and the second, which biochemical components present in the samples can provide information on the temporal estimation. Regarding the methods classes, mass spectrometry proved to be the most promising technique for fingerprint analysis, highlighting the Matrix Assisted Ionization Desorption (MALDI MS) source as the most used. With this, a MALDI MS method was developed with the application of Chemical Imaging (IMS) which, from the component’s ions selection of major intensity in the spectra, allowed the fingerprints visualization fifty days after their deposition. The second most used methods class were spectroscopy, which are mostly low-cost and non-destructive – when compared to mass spectrometry and provide results in seconds. Thus, a Micro-Fourier Transform Infrared Spectroscopy (μ-FTIR) method was developed with sebaceous fingerprints were monitored and analyzed for one week followed by application of a supervised method of Linear Discriminant Analysis. It was seen that despite the donor profiles being similar, rich in fatty acids from contact contamination, the method allowed for the elaboration of a separation trend between the samples based on the time elapsed since the deposition of the fingerprints. And, additionally, it was possible to segregate the samples by donor. Thus, this work composes a step towards the application of analytical science to Fingerprint Analysis as a foundation resource of justice in the generation of reliable evidence for the search of truth of the facts

Estudo do envelhecimento da composição química de resíduos de impressão digital latente por espectroscopia Raman

Dissertação (mestrado) — Universidade de Brasília, Instituto de Física, Programa de Pós-Graduação em Física, 2022.Cientistas forenses usam impressões digitais em investigações criminais como meio de identificação há séculos. Na ciência forense as impressões digitais encontradas em cena de crime são fundamentais para a resolução do delito. A análise desses vestígios não só pode contribuir de forma significativa para a identificação do indivíduo, mas também pode permitir que o agente policial descreva o que ocorreu, como ocorreu e quem cometeu o crime. Atualmente, não existe uma metodologia confiável de datação das impressões digitais para aplicações forenses em cenas de crime. Assim, a possibilidade de datar de forma não destrutiva impressões digitais encontradas em cena de crime seria obviamente benéfica para o aprimoramento das ciência forenses. Neste trabalho a espectroscopia Raman é usada para estudar a composição química de resíduos de impressões digitais latentes no momento em que foi depositada e as alterações químicas que ocorrem ao longo de 90 dias após deposição. Impressões digitais de 3 doadores do sexo masculino foram coletadas e envelhecidas sob condições controladas. Os espectros Raman identificaram a presença de vários marcadores químicos os quais apresentaram diferentes cinéticas de degradação. Observou-se uma contínua degradação destes marcadores a partir do progressivo desaparecimento das bandas Raman a eles associados. Foi encontrado que a taxa de degradação dos carotenoides, a qual segue uma cinética de primeira ordem e varia de doador para doador, é muito superior às dos lipídios. Os resultados mostraram que devido às suas características insaturadas, tanto os carotenoides quanto os lipídios estão sujeitos a alterações moleculares, as quais se iniciam com a isomerização das ligações duplas trans para cis, para o caso dos carotenoides, e cis para trans para o caso dos lipídios. Essas alterações levam a processo de oxidação e clivagens com a geração de subprodutos. Constatou-se que o número de ligações insaturadas nos lipídios decresce levemente nos primeiros 40 dias e então cai abruptamente. Adicionalmente, os dados Raman indicaram que os lipídios estão sendo continuamente hidrolisados ao longo do tempo de envelhecimento.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).Forensic scientists have used fingerprints in criminal investigations as a means of identification for centuries. In forensic science, fingerprints found at a crime scene are fundamental to solving the crime. The analysis of these traces can not only contribute significantly to the identification of the individual, but can also allow the police officer to describe what happened, how it happened and who committed the crime. Currently, there is no reliable fingerprint dating methodology for forensic applications at crime scenes. Thus, the possibility of nondestructively dating fingerprints found at a crime scene would obviously be beneficial for the improvement of forensic sciences. In this study, Raman spectroscopy is used to study the chemical composition of latent fingerprint residues at the time it was deposited and the chemical changes that occur over 90 days after deposition. Fingerprints from 3 male donors were collected and aged under controlled conditions. Raman spectra identified the presence of several chemical markers, which showed different degradation kinetics. A continuous degradation of these markers was observed from the progressive disappearance of the Raman bands associated with them. It was found that the rate of degradation of carotenoids, which follows first-order kinetics and varies from donor to donor, is much higher than that of lipids. The results showed that due to their unsaturated characteristics, both carotenoids and lipids are subject to molecular changes, which begin with the isomerization of the double bonds trans to cis, in the case of carotenoids, and cis to trans in the case of lipids. These changes lead to oxidation processes and cleavages with the generation of by-products. It was found that the number of unsaturated bonds in lipids decreases slightly in the first 40 days and then drops abruptly. Additionally, Raman data indicated the lipids are being continuously hydrolyzed over the aging time

Approximation of a Mathematical Aging Function for Latent Fingerprint Traces Based on First Experiments Using a Chromatic White Light (CWL) Sensor and the Binary Pixel Aging Feature

Part 1: Research PapersInternational audienceThe age determination of latent fingerprint traces is a very important challenge for forensic investigations, which has not been solved satisfyingly so far. Based on prior work, we use the novel and very promising aging feature of counting binary pixel for the approximation of a mathematical aging function to be used for the age determination of latent fingerprint traces. We first show the feasibility of this feature in a test set of nine test series (each comprised of a fingerprint sample scanned continuously over four days) using three different optical sensors (CWL) of the same model and varying resolutions (3,5,10μm). We then approximate the aging function for each test series, showing an average error of approximation between 13% and 40% for an optimal approximation. We discuss the prospects and restrictions of such a function for the age determination of latent fingerprint traces and identify future research challenges